Variable resistor having front and back stages operated by concentric shafts coupled in rotary operation by friction through a spring

ABSTRACT

In a variable resistor wherein a front-stage variable resistor operated by an outer shaft and a back-stage variable resistor operated by an inner shaft fitted concentrically in said outer shaft are coupled in the axial direction of both shafts and these shafts are coupled in rotary operation by friction through a spring which compresses against the circumferential surface of the inner shaft, said spring is made by bending an elastic wire material into a rectangular shape, the shorter sides of said spring being fixed to the end of the said outer shaft together with a brush mounting plate of the front-stage variable resistor by clinching end protrusions of said outer shaft, the said spring being penetrated by the said inner shaft, and the longer sides of said spring compressing against the circumferential surface of said inner shaft.

United States Patent Matsui et al.

[4 1 Oct. 14, 1975 Inventors: Hiroshi Matsui, Neyagawa; Tadashi Mihara, Moriguchi, both of Japan Matsushita Electric Industrial Co., Ltd., Japan Filed: Aug. 14, 1974 Appl. No.: 497,340

[73] Assignee:

Foreign Application Priority Data Aug. 20, 1973 Japan 48-97698 Apr. 1, 1974 Japan 49-37676 Apr. 1, 1974 Japan 49-37677 References Cited UNITED STATES PATENTS 6/1960 Zarrillo 338/134 III,

3,012,213 12/1961 Vaksvik 338/134 3,117,466 l/l964 Hinsey 74/531 3,462,974 8/1969 Riedel et al. 64/30 E Primary ExaminerLaramie E. Askin Attorney, Agent, or FirmBurgess, Ryan and Wayne [57] ABSTRACT In a variable resistor wherein a front-stage variable resistor operated by an outer shaft and a back-stage variable resistor operated by an inner shaft fitted concentrically in said outer shaft are coupled in the axial direction of both shafts and these shafts are coupled in rotary Operation by friction through a spring which compresses against the circumferential surface of the inner shaft, said spring is made by bending an elastic wire material into a rectangular shape, the shorter sides of said spring being fixed to the end of the said Outer shaft together with a brush mounting plate of the front-stage variable resistor by clinching end protrusions Of said outer shaft, the said spring being penetrated by the said inner shaft, and the longer sides of said spring compressing against the circumferential surface of said inner shaft.

7 Claims, 16 Drawing Figures U.S. Patent Oct.14,1975 Sheet 1 of3 FIG. I

PRIOR ART FIG. 2

PRIOR ART US. Patent Oct. 14, 1975 Sheet 2 of 3 3,913,059

U.S. Patent Oct. 14, 1975 Sheet 3 of 3 3,913,059

FIG. IIA

FIG. IO

FIG. l3

' FIG. l4

VARIABLE RESISTOR HAVING FRONT AND BACK STAGES OPERATED BY CO NCENTRIC SHAFTS COUPLED IN ROTARY OPERATION BY FRICTION THROUGH A SPRING BACKGROUND OF THE INVENTION The present invention relates to a variable resistor, and more particularly to a variable resistor comprising two variable resistors coupled to each other by a double-shaft.

In prior art double-shaft variable resistors, the operational coupling between the outer shaft and the inner shaft is effected by friction caused by a leaf spring. That is, both ends of the leaf spring fixed together with a brush mounting plate of one variable resistor to the outer shaft are bent, the utmost end thereofcompressing elastically against the circumference of the inner shaft and both shafts being coupled operationally by friction between the ends of the leaf spring and the circumfer'ence of the inner shaft, so that whenthe outer shaft is rotated, the inner shaft also is rotated. In such an arrangement, the leaf spring requires a space in the axial direction of both shafts, and therefore, it cannot be avoided that the variable resistor should be large in the axial direction. This point is a disadvantage which cannot be neglected for small variable resistors which are required to be minimized in size.

SUMMARY OF THE INVENTION An object'of the present invention is to provide a double-shaft variable resistor which is reduced in size in the axial direction and in which two variable resistors are operationally coupled by friction caused by a spring between the inner shaft and the outer shaft.

Another object of the present invention is to provide a double-shaft variable resistor in which said friction is stable.

The present invention uses a spring which is made by bending an elastic wire material into a rectangular shape instead of a leaf spring in prior art so that the circumferential surface of the inner shaft is clamped elastically between the longer sides of the rectangular spring.

According to an embodiment of the present invention, the spring is fixed to the end of the outer shaft together with a brush mounting plate of the front-stage variable resistor fixed to the outer shaft by clinching end protrusions of the outer shaft.

According to another embodiment of the present invention, the spring is contained in a groove provided on the surface of said brush mounting plate, and the brush mounting plate is fixedwith a washer to the end of the outer shaft by clinching protrusions of the outer shaft.

According to a further embodiment of the present invention, the washer in the second embodiment is omitted.

According to an additional object of the present invention, the spring is positioned by a projecting portion provided on the surface of the brush mounting plate.

The other objects and features of the present invention will be apparent from the following more particular description of this invention given with reference to the accompanying drawings. I a

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional elevation of a prior double-shaft variable resistor;

FIG. 2 is a perspective view of some essential members of the resistor shown in FIG. 1;

FIG. 3 is a sectional elevation of an embodiment of the present invention;

FIG. 4 is a perspective view of some essential members of the embodiment shown in FIG. 3;

FIG. 5 is a sectional elevation of another embodiment of the present invention;

FIG. 6A is a bottom perspective view of the outer shaft shown in FIG. 5;

FIG. 6B is a sectional elevation of the brush mounting plate of the front-stage variable resistor shown in FIG. 5;

FIG. 7 is a diagram showing the brush mounting plate, the spring and the washer shown in FIG. 5 in the assembled condition;

FIG. 8 is a plan view of the spring shown in FIG. 5;

FIG. 9 is a plan view of the washer shown in FIG. 5;

FIG. 10 is a sectional elevation of a further embodiment of the present invention;

FIG. 11A is a bottom perspective view of the outershaft shown in FIG. 10;

FIG. 11B is a sectional elevation of the brush mounting plate shown in FIG. 10;

FIG. 12 is a diagram showing the brush mounting plate and the spring shown in FIG. 10 in the assembled condition;

FIG. 13 is a sectional elevation of the brush mounting plate of an additional embodiment of the present invention; and

FIG. 14 is a diagram showing the brush mounting plate and the spring shown in FIG. 13 in the assembled condition.

DETAILED DESCRIPTION OF THE INVENTION Prior Art As shown in FIGS. 1 and 2, the frictional drive mechanism of double-shaft variable resistors in prior art is constructed by fitting end projections la of an outer shaft 1 into grooves 2a and grooves 3a to fix a leaf spring 3 placed on a front-stage brush mounting plate 2 to said outer shaft 1, and by inserting an inner shaft 4 into the outer shaft 1 so that the circumferential surface of the inner shaft 4 contacts the inside surface of the open end of the leaf spring 3 resulting in frictional engagement of the inner and outer shafts. This arrangement, however, is disadvantageous in that it can hardly be adopted for small variable resistors with space limitations owing to a fact that the leaf spring 3 requires a considerable space in the axial direction of both shafts, and moreover, the press-fitting of the inner shaft 4 into the leaf spring 3 causes the ends 3b of the leaf spring 3 to be pushed open and deformed in both longitudinal and transverse directions.

Preferred Embodiments of The Invention FIGS. 3 and 4 illustrate the first embodiment of the present invention. Referring to the figures, a frontstage mounting plate 6 and a shield plate 7 of a frontstage variable resistor 5 are fixed to each other by inserting end projections of a bearing 8 into holes in them and clinching these projections. On the lower surface of the mounting plate 6, a resistor element 9 in a horseshoe shape is fixed by an outer terminal (not shown), and moreover, a contact piece 10 is fixed by an eyelet portion 11a of a middle terminal'll. An outer shaft 12 is fitted, after being lubricated, into the bearing 8, and

projections 12a of the outer shaft 12 are inserted into grooves 13e of a front-stage brush-mounting plate 13. A frictional spring 14 is madeby bending an elastic wire material into a rectangular shape, and with the shorter elements 14a of the frictional spring 14 placed in contact with theformer-stage brush-mounting plate 13, the projections 12a of the outer shaft 12 are clinched. The front-stage brush-mounting plate [3 is mounted firmly with a brush 15-which slides on a resistance element 9. The brush 15 and the contact piece are electrically conducting at all times. An inner shaft 16 is inserted, after being lubricated, concentrically into the outer shaft 12. The inner shaft 16 penetrates a rectangular opening of the spring 14. Since the length of the shorter elements of the spring 14 is smaller than the diameter of the inner shaft 16, the circumferential surface of the inner shaft 16 is clamped elastically between the longer elements of the spring 14. v

. 'A' metallic cover 17 is made in a cap shape, and a mounting leg (not shown) provided on the periphery of the opening of the cover 17 is bent to mount on the front-stage mounting plate 6. At the bottom of the cover 17, a back-stagemounting plate 20 and a shield plate 21 are fixed by a clinching by means of an intermediate bearing 18. Through the intermediate bearing 18, the inner shaft 16 is passed, and at the end of the inner shaft 16, a back-stage brush-mounting plate 22 is fixed by clinching the end of theinner shaft 16. Numeral 23 designates a resistor element fixed on the lower surface of the back-stage mounting plate 20, and 24'designates a contact piece which is fixed to the mounting plate 20 by means of an eyelet 25a of a middle terminal 25. The contact piece 24 contacts with a brush 26 mounted on, the top surface pf the back-stage brush-mounting plate 22 in such a manner that the end of the contact piece may slide on the brush 26. Numeral 27 designates a cap-shaped metallic cover which is fixed to the back-stage mounting plate 20 by means of a mounting. leg (not shown) provided on the periphcry of the opening of the cover 27. Covers 17 and 27 are provided with depressions 17a and 27a respectively. When the brush-mounting plates 13 and 22 are rotated, these depressionsstrike bent portions 13g and 22a of the mounting plates 13 and 22 to limit rotation of respective brush-mounting plates.

When the outer shaft 12 is rotated, both the frontstagemounting plate 13 and the-brush are rotated, so. that the end (not shown) of the .brush l5islides on the surface of the resistance element 9 to change the valueof resistance appearing at a terminal 11. Similarly, when theinner shaft is rotated, the end (not shown) of the brush 26 slides on the surface of the resistance element 23 to change thevalue of resistance appearing at a terminal 25.

As mentioned above, against the circumferential surface of the inner shaft 16, the longer elements 14b of the spring 4 are compressing to result in friction between the inner shaft and the elements, so that when oneof the outer shaft 12 and the inner shaft 16 is rotated, the other'also is rotated together causing the value of resistance appearing at each terminal of both resistors to be changed. If one of the'two shafts is rotated while the other is held by hand, the value of resistance appearing at the terminal connectedto the rotated brush is changed.

FIGS. 5 to 9 to illustrate the second embodiment of the present invention. According to this embodiment,

a groove 13a and a depression 13b are providedon the lower surface of a former-stage brush-mounting plate 13. A spring 14 is contained in the groove 13a and the front-stage brush-mounting plate is fixed through a washer 28 fitted in the depression 13b to the outer shaft 12 by clinching projections 12a of the outer shaft 12.

The first embodiment is disadvantageous in that generally the endvof the wire material of the rectangular frictional spring 14 opens to weaken the clamping force on the inner shaft 16, so that the friction between the inner shaft 16 and the spring 14 may be small. Another disadvantage of this arrangement is that the position of the frictional spring 14 is brought off the center when the outer shaft 12 is clinched, or the frictional spring 14 is deformed when the inner shaft 16 is inserted into the frictional spring 14 so that the frictional torque between the inner shaft 16 and the spring. 14 may be unequal.

In contrast to the foregoing, the second embodiment of this invention is constructed in such an arrangement that the frictional spring 14 ofa rectangular shape is fitted into a depression 13a of the front-stage brushmounting plate 13, so that the frictional spring 14 may have a constant width at all times and be free from nonuniform deformations due to the press-fitting of the inner shaft 16 because the frictional spring 14 is restrained by a straight portion 13c of the depression 13a from openingoutward. Therefore, this arrangement is more advantageous than the'first embodiment in that the friction is large, and for an additional reasonthat the spring 14 is kept always at a constant position, it is stable, as compared with that in the previous proposition. Moreover, since clinching washer 28 of the outer shaft is mounted in a depression 13b provided in communication with the depression 13a in the front-stage mounting plate, the clinching portion of the outer shaft 12 is supported entirely by this washer 28 so that the possibility of deformations of the frictional spring 14 by clinching the outer shaft 12 may completely be eliminated. And with this arrangement, no difference is caused in the size of components of the variable resistor from that of the first embodiment.

FIGS. 10 to 12 illustrate the third embodiment of the present invention. In this embodiment, the spring 14 is contained in the depression 13a, and the depression 13b and the washer 28 of the second embodiment are omitted. According to the third embodiment, the function of the spring 14 is the same as in the second embodiment, but the omission of the washer 28 reduces the producing cost as compared with the second embodiment.

FIGS. 13 and 14 illustrate the fourth embodiment of the present invention. In this embodiment, projections 13d to control the positions of the four corners of the spring l4,are provided on the lower surface of the front-stage brush-mounting plate 13. When the outer shaft 12 is inserted into the spring 14 and the projections 12a are clinched on the spring 14, the four corners of the spring 14 are held by the projections 13d, and therefore the disadvantage as in the resistor shown in FIG. 1 does not occur.

What is claimed is: l

l. A variable resistor wherein a front-stage variable resistor operated by an outer shaft and a back-stage variable resistor operated by an inner shaft fitted concentrically in said outer shaft are arranged in the axial' direction of both shafts and these shafts are coupled in rotary operation by friction through a spring which compresses against the circumferential surface of the inner shaft characterized in that said spring is made by bending an elastic wire material into a rectangular shape, the shorter elements of the said spring being fixed to the end of said outer shaft together with a brush-mounting plate of the front-stage variable resistor by clinching end projections of said outer shaft, said spring being passed through by said inner shaft, and the longer elements of said spring compressing against the circumferential surface of said inner shaft so that a frictional force is produced between the longer elements of said spring and the circumferential surface of said inner shaft.

2. A variable resistor according to claim 1 characterized in that the shorter elements of the said rectangular shaped spring are smaller than the diameter of said inner shaft and the longer elements are larger than the diameter of the said inner shaft.

3. A variable resistor according to claim 1 characterized in that said spring is contained in a depression provided on the surface of said brush-mounting plate, and

said brush-mounting plate is fixed, through a washer covering said spring, to the end of said outer shaft by clinching said projections.

4. A variable resistor according to claim 3 wherein the depth of said depression is larger than the diameter of the wire material of said spring.

5. A variable resistor according to claim 1 characterized in that said spring is contained in a depression provided on the surface of said brush-mounting plate which is fixed to the end of the said outer shaft by clinching said projections.

6. A variable resistor according to claim 5 wherein the depth of said depression is larger than the diameter of the wire material of said spring.

7. A variable resistor according to claim 1 characterized in that said spring is positioned by projections provided on the surface of said brush-mounting plate, and said brush-mounting plate is fixed to the end of said outer shaft together with the shorter sides elements of said spring. 

1. A variable resistor wherein a front-stage variable resistor operated by an outer shaft and a back-stage variable resistor operated by an inner shaft fitted concentrically in said outer shaft are arranged in the axial direction of both shafts and these shafts are coupled in rotary operation by friction through a spring which compresses against the circumferential surface of the inner shaft characterized in that said spring is made by bending an elastic wire material into a rectangular shape, the shorter elements of the said spring being fixed to the end of said outer shaft together with a brush-mounting plate of the front-stage variable resistor by clinching end projections of said outer shaft, said spring being passed through by said inner shaft, and the longer elements of said spring compressing against the circumferential surface of said inner shaft so that a frictional force is produced between the longer elements of said spring and the circumferential surface of said inner shaft.
 2. A variable resistor according to claim 1 characterized in that the shorter elements of the said rectangular shaped spring are smaller than the diameter of said inner shaft and the longer elements are larger than the diameter of the said inner shaft.
 3. A variable resistor according to claim 1 characteRized in that said spring is contained in a depression provided on the surface of said brush-mounting plate, and said brush-mounting plate is fixed, through a washer covering said spring, to the end of said outer shaft by clinching said projections.
 4. A variable resistor according to claim 3 wherein the depth of said depression is larger than the diameter of the wire material of said spring.
 5. A variable resistor according to claim 1 characterized in that said spring is contained in a depression provided on the surface of said brush-mounting plate which is fixed to the end of the said outer shaft by clinching said projections.
 6. A variable resistor according to claim 5 wherein the depth of said depression is larger than the diameter of the wire material of said spring.
 7. A variable resistor according to claim 1 characterized in that said spring is positioned by projections provided on the surface of said brush-mounting plate, and said brush-mounting plate is fixed to the end of said outer shaft together with the shorter sides elements of said spring. 